VEGETATIVE AND SEXUAL REPRODUCTION 159 



reproduction. It is well known that most of the finest fruits 

 are now propagated vegetatively by budding or grafting, and 

 seedless fruits are necessarily perpetuated in this manner. 



Such plants often lose the power of sexual reproduction after 

 long cultivation and propagation by vegetative means. It is evi- 

 dent from the few examples of vegetative reproduction indicated 

 above that the higher plants, much more largely than the higher 

 animals, retain the power of reproduction by the cells in all parts 

 and organs of the body. This is probably due to the fact that 

 plants, quite unlike animals, have a long period of growth and 

 are able to renew each year the leaves and flowers of the season 

 and to increase the length of roots and stems throughout life. 



SEXUAL REPRODUCTION 



Sexual reproduction differs from vegetative reproduction in 

 the following important particulars. The reproductive cells in 

 sexual reproduction are not the ordinary unmodified cells of the 

 plant body which serve for vegetative reproduction, but are rather 

 highly specialized naked cells termed gametes. These gamete 

 cells fuse to form a new double cell, the zygote, and the zygote 

 produces a new plant by cell division. When the zygote cell is 

 formed by the union of the two gamete cells, male and female, 

 derived from different parents, the new organism which grows 

 from the zygote is quite certain to be unlike either parent, since 

 it inherits through the male and female gametes two sets of hered- 

 itary characters. The sexual process, therefore, instead of produc- 

 ing offspring like a given parent, as in vegetative reproduction, 

 is quite certain to produce a variety in offspring. In nature the 

 production of new kinds of organisms is apparently advantageous 

 to any given species, or kind, of plant in meeting the require- 

 ments of a changing environment and the struggle for existence 

 to which all organisms are subjected. Some of the new kinds of 

 offspring resulting from sexual union are quite certain to have 

 new and advantageous combinations of characters which will 

 enable their possessors to win out in the battle of plants for 

 food and light Man has taken advantage of this tendency in 



